Collecting XAFS spectra at soft X-ray energies in a heated loop cell up to 1600 K

Farges, François; Flank, A.M.; Lagarde, P.; Ténégal, F.

doi:10.1107/s0909049598017749

Cited by 6 publications

(6 citation statements)

References 3 publications

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“…The tetrahedral coordination of Si by four O atoms is a common feature of all silicates and as a consequence both crystalline and amorphous silicates exhibit very similar K-edge XANES (Li et al 1993(Li et al , 1995Wu et al 1998;Poe et al 1997Poe et al , 2004Bender 2002;Henderson & Fleet 1997;Henderson 1995;Farges et al 1999;Thompson et al 1996;Gilbert et al 2003). Typically, all show the strong white line feature G and a broad hump feature K seen in Fig.…”

Section: Si K-edge Xanesmentioning

confidence: 88%

Structural signatures of medium-range order in annealed laboratory silicates

Thompson¹

2008

A&A

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Context. Silicate dust grains exist in a wide range of astronomical environments and understanding the effect of these on grain structure is of great interest, particularly the effect of thermal annealing on amorphous silicates as a possible route to the formation of crystalline grains. Although laboratory simulations have largely focussed on IR-spectroscopic measurements, since these relate directly to observational data, laboratory synchrotron techniques such as X-ray absorption spectroscopy (XAS) and X-ray scattering are becoming increasingly routine in the analysis of recovered materials. With the increasing prospect of performing astronomical XAS observations, there is much to be gained from applying these techniques to laboratory analogues. Aims. Diagnostic markers for medium-range order and the effect of thermal annealing on these in amorphous silicates of differing Mg content are characterised using synchrotron X-ray methods. Methods. Three synthetic amorphous silicates with high, medium and low Mg:Si ratios were annealed at varying temperatures up to 1300 K. X-ray Absorption Near Edge Structure (XANES) spectra at the Si and Mg K-shell absorption edges and X-ray scattering patterns for low values of the X-ray scattering wavevector were recorded for these along with comparative data for commercially produced amorphous SiO 2 and mineral samples of forsterite, enstatite and quartz. Results. XANES features due to short-and medium-range structure are identified at both Mg and Si edges and a new temperature dependent behaviour observed in the medium-range structure surrounding Mg and Si. Based on changes to the morphological details of the XANES spectra, the medium-range structure changes between an enstatite-like and forsterite-like coordination with increasing temperature and appears to correlate directly with Mg content. Low wavevector X-ray scattering features were also found to be diagnostic of the type of medium-range structural ordering. However, these features depend on whether the relative arrangement of clusters of medium-range structure exhibit semi-periodic ordering over the longer-range, which can vary with annealing.

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Section: Si K-edge Xanesmentioning

confidence: 88%

Structural signatures of medium-range order in annealed laboratory silicates

Thompson¹

2008

A&A

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“…The structural environment of transition metals in an oxide melt above the liquidus temperature is not necessarily the same as that in a quenched glass, which was frozen at around T g , although it is often assumed to be. To study this problem directly for geochemically relevant melts, the XAFS technique was applied to study the local environment of transition metals such as Fe, Ti, Cr, Mo and Ni in oxide glasses [ 43 , 59 , 111 , 112 , 113 , 114 , 115 , 116 , 117 , 118 , 119 , 120 , 121 ]. The response of disordered systems such as glass and supercooled liquids and melts to increasing temperatures, particularly above T g , is more difficult to predict because of the variable behavior of the various components found in the glass during heating [ 111 ].…”

Section: Examples Of Using the Xafs Technique To Study The Atomic mentioning

confidence: 99%

“…In 1999, Farges et al proposed a new device to collect in situ high-temperature XAFS spectra at low X-ray energies from the K edge of Na to Cl [ 120 ]. XAFS data were collected in the fluorescence mode using a heated loop that contains the sample.…”

Section: Examples Of Using the Xafs Technique To Study The Atomic mentioning

confidence: 99%

X-ray Absorption Fine Structure (XAFS) Studies of Oxide Glasses—A 45-Year Overview

Mastelaro

Zanotto

2018

Materials

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X-ray Absorption Fine Structure (XAFS) spectroscopy has been widely used to characterize the short-range order of glassy materials since the theoretical basis was established 45 years ago. Soon after the technique became accessible, mainly due to the existence of Synchrotron laboratories, a wide range of glassy materials was characterized. Silicate glasses have been the most studied because they are easy to prepare, they have commercial value and are similar to natural glasses, but borate, germanate, phosphate, tellurite and other less frequent oxide glasses have also been studied. In this manuscript, we review reported advances in the structural characterization of oxide-based glasses using this technique. A focus is on structural characterization of transition metal ions, especially Ti, Fe, and Ni, and their role in different properties of synthetic oxide-based glasses, as well as their important function in the formation of natural glasses and magmas, and in nucleation and crystallization. We also give some examples of XAFS applications for structural characterization of glasses submitted to high pressure, glasses used to store radioactive waste and medieval glasses. This updated, comprehensive review will likely serve as a useful guide to clarify the details of the short-range structure of oxide glasses.

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“…A number of designs for X-ray spectroscopy furnaces have been reported previously. In most cases the sample is heated in a vacuum (Waychunas et al, 1988;Farges et al, 1999;Filipponi et al, 2000), air (Farges et al, 1994(Farges et al, , 1996Dent et al, 1995) or an inert gas environment (Crozier et al, 1977;Lytle et al, 1979;Jackson et al, 1993). Fe oxidation states in geological melts have been controlled over a limited range by adjusting the oxygen partial pressure with a vacuum (Waychunas et al, 1988) or using¯owing nitrogen in a furnace with Mo components to produce an f O 2 near the Mo/MoO 2 buffer (Jackson et al, 1993).…”

Section: Introductionmentioning

confidence: 99%

A furnace design for XANES spectroscopy of silicate melts under controlled oxygen fugacities and temperatures to 1773 K

et al. 2003

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A controlled-atmosphere furnace has been constructed for X-ray absorption spectroscopy experiments under imposed oxygen fugacities at temperatures up to 1773 K. The use of the furnace is demonstrated in a study of the oxidation state of Cr in a basaltic silicate melt (mid-ocean ridge basalt) by K-edge XANES spectroscopy. This is the first time the Cr(2+)/Cr(3+) ratio has been identified directly in an Fe-bearing melt. At typical terrestrial oxygen fugacities around half the Cr is present as Cr(2+), even though this oxidation state has never been identified in a terrestrial material and only Cr(3+) is observed after quenching to a glass. Cr(2+) oxidizes to Cr(3+) on cooling in the presence of Fe(3+) according to the electron exchange reaction Cr(2+) + Fe(3+) --> Cr(3+) + Fe(2+). This illustrates the importance of the in situ determination of metal oxidation states in melts.

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Collecting XAFS spectra at soft X-ray energies in a heated loop cell up to 1600 K

Cited by 6 publications

References 3 publications

Structural signatures of medium-range order in annealed laboratory silicates

Structural signatures of medium-range order in annealed laboratory silicates

X-ray Absorption Fine Structure (XAFS) Studies of Oxide Glasses—A 45-Year Overview

A furnace design for XANES spectroscopy of silicate melts under controlled oxygen fugacities and temperatures to 1773 K

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